If we just take questions that people ask on the forum then that would be copyright hell, obviously the other compnies would not give permission.
I reckon if we make trial exams it should be a community-wide effort, not just the efforts of a single individual. We could take contributions of original questions from VN members and have a study-guide team that sorts the good from the bad. To make sure the questions are original, we could have VN member's usernames underneath the questions so that if they have been copied, those members would take the blame, and not VN as a whole.
We could do the same thing for the theory section of the study guide, have a team that sorts through member contributions and collates them into an orderly study guide. The members who contribute would have glory and possibly other benefits.
I think this actually has a lot of potential if it is a community effort. Traditional study guides are at a disadvantage because they do not know what their clients need. If the community writes for the community then we will have the best chance of providing absolutely comprehensive material, and catering for everybody's needs.